1. Field of the Invention
The present invention relates to an image examination apparatus, an image examination system, and an image examination method.
2. Description of the Related Art
Prints are conventionally inspected manually, but devices that perform inspection are used recently for post processing of offset printing. When such an inspection device is used, first, a quality item is manually selected and read from among read images of a print to generate a master image. The inspection device then compares the generated master image with a corresponding part of a read image of the print to be inspected and, on the basis of the degree of the difference between the master image and the read image, determines whether there is a defect in the print.
However, plateless printing machines for electrophotography etc. is excel at smaller number of prints and, in many cases, the print contents differ according to each page in variable data printing etc. Thus, it is not efficient to generate a master image to be compared from a print as it is performed for offset printing machines. In order to deal with this problem, it can be considered to generate a master image from print data, which makes it possible to efficiently deal with variable printing.
In order to efficiently examine a read image by comparing it with a master image, alignment for correcting misalignment between the master image and the read image is previously performed. Specifically, alignment is performed in a way that reference points indicating a characteristic part of an image are extracted, the reference points are associated between the master image and the read image, and amounts of misalignment are calculated from the differences between the master image and the read image.
There is also a proposed method where an image is divided into predetermined areas and amounts of misalignment of the respective divided areas are calculated in order to analyze the tendency of the amount of misalignment over the image (see Japanese Patent Application Laid-open No. 2011-112593). There is another proposed method where an image is divided into predetermined areas and an amount of misalignment calculated for each of the divided areas is compared with an amount of misalignment of a whole image in order to calculate the amount of misalignment over the image (see Japanese Patent Application Laid-open No. 2011-252886).
However, when a read image has a print defect occurring in a position serving as a reference point or has the same repeated pattern, it is difficult to find reference points corresponding to those of the master image, which may results in a failure in alignment using reference points. According to Japanese Patent Application Laid-open No. 2011-112593 and Japanese Patent Application Laid-open No. Japanese Patent Application Laid-open No. 2011-252886, a failure in such alignment is not taken into consideration. In other words, when such a failure in alignment occurs, the amount of misalignment of each divided area is miscalculated, which results in erroneous alignment.
Therefore, there is provided a need to prevent, when examining a read image by comparing it with a master image, a failure in alignment between the read image and the master image.